Fluid flow rate control mechanisms are utilized in a variety of flow systems in order to control the amount of fluid such as, for example, gas or liquid, passing through a flow system. Flow control mechanisms can be utilized to regulate flow rates in systems such as ventilators and respirators for maintaining a sufficient flow of breathable air or providing sufficient anesthetizing gas to a patient in preparation for surgery. Typically, flow rate control occurs through the utilization of control circuitry responsive to measurements obtained from fluid flow sensors. Such a fluid flow sensor may be configured to measure properties of a fluid in contact with the sensor and to provide output signals in response to the fluid flow rates in a flow channel.
Additionally, these flow sensors may measure a flow rate by sampling a fluid by means of a bypass flow channel in parallel with a flow restrictor placed in the main flow channel. Fluid flow sensors can be utilized in a variety of fluid-sensing applications for detecting the movement of fluids. Such fluid-sensing applications may include, but are not limited to, industrial, commercial, medical and automotive industries. For example, an airflow sensor is often employed in the medical industry to monitor and/or control a patient's breathing. Similarly, an airflow sensor might also be employed in a valve to control ratio of gas mixing prior to combustion. Such flow sensors are susceptible to mis-measurement due to turbulent flow effects (e.g., non-uniformity in flow velocity and pressure), and thus the accuracy of such sensors may be adversely affected by such factors.
The majority of prior art mass-flow sensors require additional pressure restriction in the flow path, especially in a bypass, in order to limit the amount of fluid flow through the sensor and avoid output saturation. These types of flow restrictors may include the use of one or more sintered metal restrictors or orifices, such as, for example, machined sapphire orifices, which are typically installed into a flow path of a flow channel. Such sintered restrictors and orifices are costly to manufacture. Orifices produce a flow jet, which can lead to an increase in flow turbulence. Therefore, it is desirable to provide an airflow sensor that incorporates the use of one or more improved flow restrictors and which is capable of accurately and reliably measuring fluid flow in a stable and turbulence-free manner.
In an effort to address the foregoing difficulties, it is believed that a need exists for an improved and inexpensive flow restrictor that laminarizes flow and reduces flow turbulence. It is believed that the improved flow restrictor disclosed herein can address these and other continuing needs.